Tricycle constructions are designed optimally to provide both lateral and longitudinal stability. Upon consideration, it will be apparent that weight placement (the rider's weight) along the longitudinal axis of the central frame section will greatly affect both lateral and longitudinal stability. Obviously, if the rider's weight be placed above the front wheel, both lateral and longitudinal stability would be lost. Likewise, if the seat were to be placed directly above the rear wheels, longitudinal stability would essentially be lost.
Instability occurs therefore to a greater or lesser extent when the tricycle seat is made adjustable to accommodate different sizes of riders. Usually such adjustments are purposely quite limited along the longitudinal axis of the central frame since space is limited and because of the possibility that more than limited movement will produce excessive instability.
Various solutions respecting seat positioning can be seen in U.S. Pat. Nos. 1,598,869; 3,096,100; and 3,123,379. Although each of these patents discloses some means for moving a tricycle seat longitudinally, in each case such movement is independent of the rear wheels. It is the purpose of the present invention to disclose a tricycle construction where seat and rear wheels may be shifted longitudinally as a unit, and furthermore to disclose means to vary not only seat position but overall body length of the tricycle.